The present invention is directed to a conveyor system switch for control of conveyor travel between two travel paths, and, in particular, to a switch that employs a tubular linear induction motor for driving of the switch mechanism.
Conveyor systems, such as power and free systems, typically have multiple tracks that are connected to each other, wherein a switch plate is employed that travels between first and second positions for directing a conveyed article from one track to another. Switch plates typically comprise a pivoting switch member having upper and lower tongues on one end, and a driving arm on the other end, wherein the upper and lower tongues are adapted to abut upper and lower track flanges to cause the article to be diverted to the appropriate track. In this manner, the switch plate functions to move between first and second positions, to divert the article being conveyed from one path to another, similar to a switch on a railroad track.
Various types of conveyor switches, like the one described above, have been used in past conveyor systems, including the one shown in U.S. Pat. No. 4,542,698. This patent discloses a switch powered by a hydraulic drive. One problem with prior systems of this type, however, is the complexity of the pipes, supply systems and compressors required for operation. Another problem is the high maintenance required to keep such systems in operation.
In view of the drawbacks of prior conveyor switches of the kind described above, a need has developed to provide an improved switch. The present invention solves the above problems through the use of a tubular linear induction motor as the switch drive. The present invention also contemplates using a mounting and/or connecting means to account for the arcuate movement of the switch member as it pivots.
The present invention represents an improvement over previous conveyor switches, and in particular, conveyor switches such as those that direct a moving conveyor component between two paths of travel, the switch including a switch tongue driven between first and second positions by a switch drive. Like previous conveyor switches, the present invention functions to divert conveyor components, such as trolleys, to one of two paths, wherein a pivoting switch member having upper and lower tongue members for engaging upper and lower track flanges are provided to cause the conveyor components to be diverted.
In one aspect, the present invention represents an improvement over previous switch designs in that it comprises a tubular linear induction motor as the switch drive for moving the switch member between the first and second positions. The linear induction motor preferably comprises a stationary primary, which can be provided with fins for better heat dissipation, and a moving secondary, such as a metal rod, extending linearly within the stationary primary. In this respect, the linear motion of the rod through the primary, from a retracted position to an extended position, and vice verse, is preferably induced by a sweeping magnetic field along the length of the primary, wherein the magnetic field interacts with currents induced within the secondary to provide a driving force to the rod. By reversing the sweep of the field, the travel direction of the rod can be reversed. The linear induction motor has fewer moving parts, is easier to maintain, and avoids the need for complicated hydraulic or pneumatic pipe systems.
The induction motor of the present invention can also be provided with one or more holding coils that can be employed to retain the secondary in a given position. For example, a holding coil can be employed on one side of the primary to maintain the secondary in the extended position, wherein the tongue members would then be positioned to cause the article to travel along one path. Another holding coil can also be provided on the other side of the primary to maintain the tongue members in the retracted position, wherein the tongue members would then cause the article to travel along the other path. The holding coils make it possible so that the induction motor does not have to be continually powered. By powering the motor for only a short period of time, motor life is increased and motor heat generation is minimized. The switch member can also include control components to interface the switch with other components of the conveyor system and their respective control features.
The switch member of the present invention preferably pivots about a single point. Therefore, the link between the switch member and its drive mechanism travels along an arcuate path, which is in contrast to the linear movement of the drive rod traveling between the extended and retracted positions. In this respect, the inventive switch is preferably adapted so that the arcuate movement of the link is accounted for by one of several mounting and/or connecting means, wherein side loading of the drive rod (which can cause abnormal wear to occur as the switch is repeatedly activated) can be avoided.
In one embodiment, the switch motor is allowed to rotate as the drive rod moves between the extended and retracted positions. In this respect, the motor is preferably mounted on a plate having a pivot pin extending therefrom, wherein the pivot pin is connected to a mounting frame with a low friction slide plate extending therebetween. In this embodiment, the pivot pin preferably has its vertical axis extending through the center of the drive rod, such that no eccentricity is created between the pivot pin and rod when the motor is rotated.
In another embodiment, the switch motor is mounted on a vertical trunnion with pivot pins extending above and below the motor to allow the motor to rotate. The entire motor with the trunnion tube is allowed to rotate in response to the switch member""s arcuate movements. The pivot pins in this embodiment also have their vertical axis extending through the center of the drive rod for similar reasons.
In another embodiment, the drive rod is provided with a coupling that allows the distal end of the rod to move freely in relation to the remainder of the rod. In this respect, the coupling is capable of separating the movement of the link from the rod, such that while the portion of the drive rod within the primary moves linearly, the end of the rod connected to the link can move along an arcuate path.
In another embodiment, the switch motor is mounted onto a mounting frame, and a guide bar is provided to maintain the drive rod along a linear path. The connection between the drive rod and switch member is preferably provided with a slotted groove, to allow the link to move in relation to the rod, such that the link can follow an arcuate path, while the rod follows a linear path.
The four embodiments discussed above are examples of how the arcuate movements of the link can be accounted for by the present invention. Other ways, not mentioned herein, which provide similar functions, are also within the contemplation of the present invention.